Well, I planted my first ever spuds this year - I got a couple of bags of seed pots from the bargain bin at the garden centre for 99p each! One bag of Anya (salad spuds) and the other Desiree (maincrop). I put them in egg boxes on the windowsill for a month or so, and planted them when they had sprouted in about mid April - as soon as I'd got the (virgin) ground dug over. I earthed them up a couple of times, and had a fair few Anya, and about 30lbs of Desiree (from a bed 4'x12' ish). I didn't prepare the ground the autumn before, as I only got the plot in April, but I've lobbed lots of horse manure on next year's bed, and covered it with black plastic.
One of my plot neighbours planted the supermarket spuds that I'd left in a cupboard for a bit too long (they had long white sprouts on), and got a crop, but he planted them too close together in my view, and didn't get a good yield. One of my books says that shop bought spuds are often treated with agents to stop or slow sprouting, so may not be very vigorous.
Hope this is some help!